Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow

[Doug Doan]

On 06/03/2010 11:11 AM, Andrew Morton wrote:
> On Thu, 3 Jun 2010 10:36:00 -0700
> Doug Doan<dougd@xxxxxxxx>  wrote:
>
> > > Well, specifically it means that
> > > mmu_notifier_invalidate_range_start/end() implemetnations can no longer
> > > take page_table_lock or any lock which nests outside page_table_lock.
> > > That lessens flexibility.
> > >
> > > As the other mmu_notifier_invalidate_range_start/end() callsite in this
> > > function carefully nested those calls outside page_table_lock, perhaps
> > > that was thought to be a significant thing.
> >
> > Here's my rationale: for the normal page case, the invalidation call is done
> > inside a page_table_lock,
>
> It is?  Where does that happen?

handle_pte_fault() acquires the lock before calling do_wp_page():

        ptl = pte_lockptr(mm, pmd);
        spin_lock(ptl);
        if (unlikely(!pte_same(*pte, entry)))
                goto unlock;
        if (flags & FAULT_FLAG_WRITE) {
                if (!pte_write(entry))
                        return do_wp_page(mm, vma, address,
                                        pte, pmd, ptl, entry);
                entry = pte_mkdirty(entry);
        }

do_wp_page() calls set_pte_at_notify(), which either calls 
mmu_notifier_change_pte() or mmu_notifier_invalidate_page().

> > so the same should also be done in the huge page case.
> > Does it really make sense to call invalidation on one hugepage and have another
> > call invalidate the same hugepage while the first call is still not finished?
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